The present invention relates generally to telecommunication services and more particularly to a method and an apparatus for more effectively utilizing fiber-optic cable splice protector closures.
Fiber-optic communications cable systems are becoming widely used in the communications industry because of the increased data throughput capacity. For example, a fiber-optic cable has a throughput capacity that exceeds 40 times that of conventional metallic cables. Accordingly, fiber-optic cables are very desirable for use in densely populated metropolitan areas and for transporting data and information in today""s communication age. The use of fiber-optic cables is also advantageous because they are immune from losing information due to random electromagnetic pulses. One reason for this advantage is that fiber-optic cables use light pulses instead of electrical signals to carry information. A disadvantage of using fiber-optic cables, however, is that they are not as readily detected by conventional metal and electrical signal detectors. Thus, cable detection systems may not be used to detect fiber-optic cables. This disadvantage of fiber-optic cables poses a number of risks and maintenance difficulties not posed by metallic cables. For example, fiber-optic cables are relatively vulnerable to the risk of being cut during construction.
It is also often necessary to detect a fiber-optic in order to find detected problems, to carry out repairs and to connect other cables. In general, it is nevertheless imperative to be able to detect cabling for repair, replacement or maintenance to avoid extended disruption of service of any kind and to maintain a high grade and quality of service for both voice and data transmissions.
To enhance or enable detection of fiber-optic cables, fiber-optic cables are often formed within a metallic sheath. Alternatively, a tracer wire is often embedded in the fiber-optic cable bundle. A low frequency electrical signal, known as a tone, is transmitted from a central office down the sheath or tracer wire to enable detection. In order to conduct the tones along the cable, however, the sheath or tracer wire of the fiber-optic cable bundle cannot be directly grounded at any point except at a terminating end. Otherwise, the signal will not travel the entire length of the cable and will render portions of the fiber-optic cable bundle undetectable.
In some communications cable systems, the fiber-optic cable bundle can be as long as 100 miles in length. Such a lengthy cable bundle typically has a large number of xe2x80x9cside legs.xe2x80x9d A side leg is a cable or cable bundle that branches from the main cable bundle and serves a smaller group of users. These side legs often vary in length. As a result, they also vary in impedance. Due to the potential differences in impedance caused by differences in side leg lengths, it is likely that a cable locating tone will propagate at different, and sometimes insufficient strengths, down each side leg. If the tone has insufficient signal strength, radiation of the tone may not propagate to the surface above the buried cable with sufficient strength to be readily detected or detected at all. Accordingly, proper design of tone detection systems is very important.
On occasion, a fiber-optic cable bundle must be strung over and above major roadways and other obstacles. The conductive metallic sheaths or tracer wires are therefore subject to transient electrical surges induced from any number of sources, including lightning. The transient electrical surges on the cable can cause damage to equipment connected to the cable and can also be very dangerous to persons working on, or otherwise coming into contact with the cable. Accordingly, there is a great need to ground the metallic sheath or tracer wire, with respect to transient surges, to minimize danger to people and equipment.
The length of ground cable extending from the fiber-optic cable bundle to ground also presents physical hazards that can easily damage the fiber-optic cable bundle. For example, they can become tangled with an animal, person or moving object, causing undue force to be exerted against the fiber-optic cable bundle to which the ground cable is attached. To illustrate, a person may trip over the wire, thereby exerting a severe tug on the fiber-optic cable bundle. Similarly, the cable can become tangled with a moving vehicle, grass mower blades and the like.
In addition to the dangers from exposed grounding cables, any sudden pulling force can damage the fiber-optic cable closure or the cable bundle, either of which consequence can require disruption of communications services until repaired. Disruption of service typically can cost a communications service provider large amounts of revenue, often exceeding one million dollars per hour. Thus, while it is important to ground a fiber-optic cable sheath, there are many risks involved with doing so.
One problem with merely grounding the metallic sheath or tracer wire, however, is that the grounded wires would also serve to ground and prevent propagation of the tones. Thus, while there is a need to avoid grounding the cable so that tones will conduct along the entire length of the fiber-optic cable bundle, there also is a competing need to consider the safety issues of not grounding a metallic sheath or tracer wire.
One solution that reconciles the competing needs is to install a surge suppressor at the termination site of each customer drop, connected between either the outer sheath or tracer wire of the cable and a ground. The surge suppressor operates as a short circuit to a local ground, for transient signals exceeding a specified threshold. Otherwise, the surge suppressor operates as an open circuit allowing the tones to be conducted down the line. The use of the surge protectors, therefore, offers an elegant solution to most of the problems listed above. Unfortunately, several problems continue to exist.
While surge protectors act as an open circuit to tones as they propagate down the metallic sheath or tracer wire, they typically are secured on or near the cable sheath under the ground level to connect the sheath to a grounding rod. Access to and retrieval of the buried sheath and protector block replacement, for maintenance and the like, are typically gained through a manhole or hand hold. Preferably, the connection between the ground cable and sheath is made within a protective closure which is retrieved as well. The ground cable between the grounding rod and the surge protector varies in length, but is typically at least fifteen feet long, to allow the surge protector and closure to be more conveniently located away from the manhole or hand hole for service. Having long grounding cables is problematic, because increased length increases cable resistance, thereby diminishing grounding effectiveness.
The fiber-optic protective cable closure is a housing device that protects and maintains the integrity of fiber-optic cable splices and connections to the ground cables and the surge protectors. In some systems, the surge protector is placed above ground in a pedestal while the closure is placed below ground in the manhole.
Conventional systems include long grounding cables that connect the surge protector to the sheath. Accordingly, when the surge protector or the protective closure need repair or maintenance, they are removed to a convenient location. Accordingly, a long grounding cable is required so that the grounding cable does not have to be cut and re-attached during the repair or maintenance. Pulling a long grounding cable through the manhole to repair a fiber-optic cable bundle creates an additional step. Moreover, a person repairing the closure or fiber-optic cable bundle will also frequently coil the grounding cable. This is often done to reduce the danger of tripping on the grounding cable or the danger of the grounding cable becoming tangled with a moving object. Thus, having a long grounding cable creates yet another step. Moreover, significantly reducing the length of the grounding cables can save tremendous amounts of money when one considers the cumulative effect of reducing all of the grounding cables even for only one 100-mile fiber-optic cable bundle loop.
Thus, a need therefore exists for an apparatus and method of connecting fiber-optic cable bundle metallic sheaths or tracers wires to a grounding rod with grounding cables that are as short as possible.
Because splices of fiber-optic cables within a protective closure can typically carry millions of dollars worth of communications per hour, damage to the splices can result in a staggering amount of lost business and resulting lost revenues. As a result, defective surge protection systems are often not repaired or maintained, due to a strong desire to minimize inadvertent damage to the splices within the closure. Accordingly, many cable location systems are inoperable, because the tones cannot be effectively transmitted down a fiber-optic cable bundle that has not been properly maintained.
A need therefore exists to reduce the risk of inadvertent damage to the splices within the closure during routine maintenance of fiber-optic cable bundle systems.
A need also exists to facilitate fiber-optic cable bundle maintenance, that increases efficiency and safety, and that reduces costs of labor and materials.
A typical fiber-optic cable bundle system, according to the present invention, includes a quick disconnect for mechanically disconnecting a closure or surge protector from a ground rod. The quick disconnect is connected in between one or two short grounding cables. One grounding cable is connected to a closure or surge protector and the other is connected to a grounding rod. The grounding cable that connects the quick disconnect to the closure is electrically coupled to one of a metallic sheath or a tracer wire for transmitting tones down the length of the cable bundle.
Including a quick disconnect between the surge protection circuitry and the grounding rod allows the use of relatively short grounding wires. Because a fiber-optic cable bundle can be disconnected from the grounding wire, there is no need to have a long grounding cable for repair or service in a convenient location. Additionally, efficiency is increased in that the grounding cable no longer needs to be pulled and coiled. Material costs are also reduced.
In an alternate embodiment of the invention, the quick disconnect also is placed serially between the surge protection circuitry and the closure. This allows the surge protection circuitry to be separated from the closure. Accordingly, it is less likely that the closure will inadvertently be damaged during the servicing of an ancillary circuit such as the surge protector or filter. This facilitates the maintenance and repair of the fiber-optic cable systems.
Another aspect of the invention is to include the quick disconnects between the surge protection circuitry and other external fiber-optic cable bundle system components. For example, the quick disconnects are, alternatively or in combination, placed serially between the surge protection circuitry and components such as pull blocks, pedestals and water proof enclosures. The inclusion of the quick disconnects between the components of a fiber-optic cable bundle system creates modularity in that the components can readily be separated electrically and mechanically. The use of the quick disconnects protects splicing within the closure when either a component or the surge protection circuitry is serviced or when a component experiences a sudden tugging motion from another source. This modular feature eliminates a risk and disincentive to service fiber-optic cable bundle system components, such as the surge protection circuitry.
In another aspect of the present invention, a new and improved closure allows electrical access to the internal components without opening and potentially damaging the splices or components within a closure. More specifically, external ports create a connection to specified electrical contact points within the closure. In one embodiment, a port is connected to the sheath or tracer wire of the fiber-optic cable bundle. In another embodiment, a port is connected to at least one sensor within the closure wherein the sensor is for monitoring either a vacuum level, a humidity level, a specified voltage level or is any one of other common sensing devices. In yet a third embodiment, a port is connected to circuitry that monitors communication signals being transmitted within the closure.